Re: Lighting questions

[Robert Myers <rmyers@inetone.net>]

At 09:31 AM 8/7/98 PDT, you wrote:
>>
>>Scott, IME, stock wiring is simply not heavy enough to carry such loads 
>for
>>any length of time
>
>Why?  

I've BTDT.  I inserted higher wattage bulbs in the fog lights of an '88
90q.  Shortly thereafter I had no fog lights due to burnt out wires or a
connector somewhere.  I never resolved which.  My wife totalled the car
shortly after the fog lights died.  New light bulbs did not solve the
problem.  Calculations be damned.  The wiring (including/or the various
connectors?) simply ain't up to the job.

>I've followed threads endlessly, downloaded proposed wiring 
>diagrams from other sites, but never seen an analysis of stock wiring.  
>My high beams are powered from the wimpy switch by one 12 Ga. wire, then 
>two fuses feed two 14 Ga. wires that go to the bulbs, then two 14 Ga. 
>wires to ground.  I'm on the road and can't look this up, but I believe 
>14 Ga. wires are rated for 15 amp applications (?).  

Could be.  15 amps at 12 volts = 180 watts - MAXIMUM.  A 100 watts lamp at
12 volts draws 8.3 amps or nearly 60% of the rated maximum load for the
wire.  Now, throw in a resistive connection or two and some IR drop in the
wire itself and the heat produced by current flowing through that
resistance and the next thing you know insulation is melting.

How many have tried these plug-in high wattage 9004 lights?  I have on one
of my '89 200tqs.  They kept burning up bulb sockets at the ground
connection.  It was so bad that I went back to stock and then added fog and
driving lights.  (Incidentally, these were the sockets supplied by
Competition Unlimited, not stock Audi sockets.  They were significantly
longer lasting than the stock sockets.)  Slightly resistive connection +
current -->  HEAT.  (Watts = I^2*R.)  This localized heat will definitely
burn stuff up.  Again, BTDT.

>That's about 200 
>watts at normal alternator voltage per wire, plus an unknown safety 
>factor (usually pretty high for automotive).  That rating also takes 
>into account momentary spikes.  Hella cites up to ten times the power 
>rating for their bulbs on start up, other applications may draw even 
>more, and the wires are rated for those normal applications.  What about 
>the connections?  These same connectors are used for much higher loads 
>elsewhere.  I agree there are line losses, after ten feet of wire you 
>should jump to the next Ga. wire, and I'm close to ten feet.  My bulbs 
>may run a little cooler and last a lot longer.

And produce less light.

>How much difference does heavier wiring make in headlight performance?  

You do the calculations.  If there is enough IR drop in the wiring before
(or after for that matter) the light then the current through the filament
will be decreased and light output (rather closely proportional to I^2*R)
will decrease in correlation.  13.4 volts, at the light, will be
significantly brighter than 12.0 volts.  The difference between 13.4 volts
and 8 volts will be even more pronounced.

>No one has cited any measurements, just subjective opinions.  

I recall a number of posts which reported measured voltages at the light
socket.  These measurements have been done, I think.  No, not by me.

>I spent a 
>lot of years making automotive and electronic optics, I saw a lot of 
>production and maintenance workers try to fix problems with the product, 
>and convince themselves they saw an improvement without measuring it.  
>It's easy to do, I've done it.  I usually got called by QC at 2:00am to 
>resolve the problem and help throw away several hours of bad product.  
>What's a small increase in headlight brightness worth?  In low-vis, poor 
>optics will throw even more blinding light where you don't need it and 
>make your fog lights even less helpful.  If you have good optics, you 
>don't need an incremental increase in brightness.

Agreed, good optics help greatly.  The lights in my S6 are almost
infinitely superior to my '89 200tq.  Optics makes the difference.

The desirability of incremental increase is, of course a matter of opinion.
 If you spend your entire life driving only during the daytime you don't
need lights at all, much less an incremental improvement.  If you drive
only on well lighted city streets you almost don't need lights.  If you
drive on totally dark country roads, every little bit of extra light you
can get is a help.  Especially as you age and your night vision begins to
suffer age related deterioration.  BTDT, also.  :-(

Am I satisfied with the lighting on the S6?  Well, it's certainly much
better than those on the 200.  Enough so that I can probably live with them
for a while.  Until, that is, I can find a good way of mounting some good
100 or 130 or 180 watt fog lights and driving lights in an unobtrusive spot.

>I'm not an EE, I really don't understand electrons as well as I should.  
>I appreciate the dire warnings and many other tips, and I'll appreciate 
>anyone telling me why I'm wrong and saving me a whole lot of trouble and 
>$.  Luckily I usually wear nomex for my 400 mile weekly commute, maybe I 
>need to move my fire extinguisher out of the trunk?

No flames, Scott.  You are certainly free to do whatever you want.  It's
your car.  I was simply trying to relate my experiences.  I wish you
success with your lighting mods.

>Scott
>'90 200tqw


___
   Bob
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